Transporting Spent Fuel: Protection Provided Against Severe Highway and Railroad Accidents (NUREG/BR-0111)

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Publication Information

Date Published: March 1987

Author:
William R. Lahs

Division of Regulatory Applications
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Introduction

This report summarizes the results of a study conducted for the Nuclear Regulatory Commission (NRC) to determine the level of safety provided during shipments of spent fuel from U.S commercial nuclear power plants. The study focuses on the protection provided for shipments that may be involved in truck or railroad accidents.

During shipment, the cask and the form and structure of the spent fuel being shipped provide the primary physical means for containing radioactivity and for limiting radiation levels outside the cask. These functions must be maintained at acceptable levels even under the wide range of forces the cask and fuel could be subjected to during an accident.

Spent fuel shipments are regulated by both the Department of Transportation (DOT) and the NRC. The NRC evaluates and certifies the design of the shipping casks used to transport spent fuel, while DOT regulates vehicles and drivers.

Current NRC regulations require that shipping casks meet certain performance standards. The performance standards include normal operating conditions and hypothetical accident conditions a cask must be capable of withstanding without exceeding specified acceptance criteria that (1) limit releases of radioactive material and radiation levels outside the cask and (2) assure that the spent fuel will remain subcritical (that is will not undergo a self-sustaining nuclear reaction).

The study, conducted by Lawrence Livermore National Laboratory (LLNL),^* began with an assessment of the possible mechanical and/or thermal forces generated by actual truck and railroad transportation accidents. The magnitudes of forces from actual accidents were compared with forces attributed to the "regulatory-defined" hypothetical accident conditions. The frequency of the accidents that can produce defined levels of thermal or mechanical forces was also developed. With this information, the study results show that for certain broad classes of accidents, spent fuel casks provide essentially complete protection against radiological hazards. For extremely severe accidents, those that could conceivably impose forces on the cask greater than those implied by the hypothetical accident conditions, the likelihood and magnitude of any radiological hazard were conservatively calculated. The study also contains an evaluation of the radiological risk from transportation accidents. Risk represents the summation of the products of the magnitude and likelihood of all accident outcomes. The purpose for making the risk calculations was to compare the resulting values with those previously used by NRC in judging the adequacy of its regulations.

The purpose of this summary, prepared by the NRC staff, is to present the results of the LLNL study to a broad range of readers who may possess varying degrees of knowledge on the technical subjects covered in the LLNL technical report. As a result, this summary focuses on the overall approach and major results of the study. Although this summary describes many important assumptions and insights, a complete understanding of the scope and meaning of the LLNL work would require, as a minimum, frequent reference to the main LLNL report and its supporting appendices.

For the reader interested solely in the results of the LLNL study, the figure on the next page, the foldout on page 29, and the discussion under "Summary of Objective and Results" should be consulted. Readers wishing to understand the logic of the approach and the basis for major assumptions should refer to the main body of this summary report, which presents a step-bystep explanation of the separate tasks required to meet the study's objectives.

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^* "Shipping Container Response to Severe Highway and Railway Accidents," NUREG/CR-4829, February 1987. This report underwent peer review by the Denver Research Institute. The LLNL report and documentation resulting from peer review are available for inspection and copying at the NRC Public Document Room, 1717 H Street, NW, Washington, D.C. Formal NRC reports are available for purchase through the Superintendent of Documents, U.S. Government Printing Office, Post Office Box 37082, Washington, D.C. 20013-7082.